THE PERFORMANCE LIMIT OF COHERENT OTDR ENHANCED WITH OPTICAL-FIBER AMPLIFIERS DUE TO OPTICAL NONLINEAR PHENOMENA

This paper theoretically and experimentally clarifies the limit of inc ident optical pulse power in coherent optical time-domain reflectometr y (C-OTDR) enhanced with optical fiber amplifiers. The critical pulse power, at which the performance of C-OTDR is degraded by the effect of optical nonlinear phenomena in a single-mode optical fiber, depends o n the amplified optical pulse waveform and the pulse width. For a puls e width of 1 mus or longer, the incident pulse power is limited by the effect of self-phase modulation (SPM). When an optical pulse having a power gradient within the pulse width is incident to a single-mode op tical fiber, the optical frequency of the backscattered signal is shif ted by SPM, and the center frequency of the signal moves outside the r eceiver band, so the sensitivity of C-OTDR is degraded. For a pulse wi dth of 100 ns, the incident optical pulse power is limited by four-wav e mixing (FWM) which transfers the energy from the incident optical pu lse to Stokes and anti-Stokes light as a result of the interaction bet ween the incident optical pulse and amplified spontaneous emission. Th is paper also demonstrates the high performance of C-OTDR enhanced wit h EDF A's with 48, 44, 39, and 29 dB single-way dynamic ranges for pul se widths of 10 mus, 4 mus, 1 mus, and 100 ns, respectively, limited b y the effect of SPM or FWM. These results are believed to be the best performance of C-OTDR with EDFA's.